Ink jet recording head

Abstract: An ink jet recording head that is formed by laminating a plurality of thin plate members (108,112,118), each having a plurality of holes (109,114,121). The holes (109,114,121) of the adjacently stacked thin plate members (108,112,118) cooperate to form ink flow paths each continuously extending to communicate a nozzle opening (131) with a respective pressure producing chamber (103), which is connected to an ink supply section (110). In such ink jet recording head, the holes (109,114,121) can be aligned or shifted with respect to each other, and allow ink to flow smoothly, thus preventing stagnation of air bubbles contained in the ink within the print head. Further, the nozzle openings (131) are arranged in arrays (A,B,C,D,E,F) in an auxiliary scanning direction. The nozzle opening arrays (A,B,C,D,E,F) are divided into three groups (20,202,203) spaced apart from each other at a predetermined interval in a main scanning direction. Nozzle openings (131) belonging to groups (202,203) arranged on both sides of the middle group (201) are positioned vertically between adjacent nozzle openings of the middle group. A nozzle opening of the middle group (201) is positioned uppermost or lowermost in the auxiliary scanning direction, so that lines printed by the nozzle openings belonging to the groups (202,203) arranged at both sides interpose a line printed by the nozzle openings of the middle group (201) to reducing inter-line error due to misalignment of the recording head with respect to a printing sheet.

Description: The invention relates to an ink jet recording head having a plurality of nozzle openings disposed in a sheet forwarding direction, with each nozzle opening jetting an ink droplet due to pressure provided by a pressure producing chamber. More particularly, the invention is directed to a nozzle opening arrangement on the ink jet recording head. Ink jet recording heads are widely used throughout the printing industry. Such ink jet recording heads exhibit high recording density, are capable of printing dots of various sizes, and are relatively quiet during operation. Two basic types of ink jet recording heads exist. A bubble jet type recording head uses thermal energy provided by a heater to effect printing. On the other hind, in a piezoelectric vibration element driven recording head, the displacement of piezoelectric vibration elements causes ink to be emitted to effect printing. Two general types of piezoelectric vibration element driven recording heads exist. In the first type, vertical vibration of the piezoelectric vibration elements causes ink to be emitted. In the second type, flexural vibration of the piezoelectric vibration elements causes ink to be emitted. In the first type of piezoelectric vibration element driven recording heads, the area in which a piezoelectric vibration element abuts against the vibration plate can be reduced. Hence, the interval between the nozzle opening arrays can easily be made small. However, the process for assembling such a recording head is complicated because each piezoelectric vibration element is extremely small. The second type of piezoelectric vibration element driven recording heads employs a laminated structure, ouch as described in Japanese Unexamined Patent Publication No. 4-366643. That is, a common ink supply section, and pressure producing chambers or ink flow paths, are first formed in each of a plurality of thin plate members. These thin plate members are then sequentially laminated on the back of a nozzle plate. Accordingly, the assembly process is simple. However, in this arrangement, each flow path extending from the pressure producing chamber to the nozzle openings is formed by making communicating holes in each thin plate member, and arranging these communicating holes proximate to one another. Hence, it is difficult to discharge the tiny air bubbles in the ink from the corners of the flow paths formed in each thin plate member. In addition, in this arrangement, the size of the piezoelectric vibration plate mounted on the pressure producing chamber is larger than that of the piezoelectric vibration plate used as the piezoelectric vibration element in the first type of piezoelectric vibration element driven recording head. Hence, the distance between the nozzle opening arrays is increased. If the distance between the nozzle opening arrays is increased, error between dots printed on a recording sheet in the auxiliary scanning direction tends to increase if three or more nozzle opening arrays are formed in an attempt to improve printing quality. In this case, however, printing quality is actually reduced. That is, a recording head having a plurality of nozzle opening arrays is designed so that each nozzle opening array enables a dot to be printed at a predetermined position in the auxiliary scanning direction. As a result, this type of recording head has the uppermost nozzle opening and the lowermost nozzle opening arranged at opposite ends in the main scanning direction. This causes an error of G x sin between lines in the auxiliary scanning direction before and after sheet forwarding, assuming that the distance between the nozzle opening array at one end and the nozzle opening array at the other end in the main scanning direction is G, and the angle of inclination between the direction in which the nozzle opening arrays of the recording head extend and the sheet forwarding direction is . This error, G x sin , causes white lines and black lines to be intermingled during printing, thereby impairing painting quality. An ink jet recording head designed to eliminate this problem is described in EP-A- 554907. In this ink jet recording head, four nozzle opening arrays, each having a plurality of nozzle openings linearly pitched in the sheet forwarding direction at an interval corresponding to the number of nozzle opening arrays, have their positions in the main scanning direction staggered by a predetermined interval so as to be different from the physically arranged sequence thereof. This arrangement, which reduces the distance in the auxiliary scanning direction between the uppermost nozzle opening and the lowermost nozzle opening of the recording head, can prevent printing of white lines and black lines due to displacement in the angle  between the nozzle opening array and the sheet forwarding direction. However, this advantage is realized only when the number of nozzle opening arrays is four. Hence, such a design is applicable to a limited number of recording heads. Prior art document GB-A-2 182 611 discloses an ink jet recording head comprising a plurality of thin plate members each having a plurality of holes therein, said thin plate members being laminated together so that said holes formed in adjacent said thin plate members are aligned with each other and cooperate to form a plurality of ink flow paths each continuously extending from a respective nozzle opening to a respective pressure producing chamber which communicates with an ink supply section. The area of a hole of a plate member, which is adjacent the nozzle plate, is smaller than the area of another hole of another plate member. It is an object of the present invention to provide a laminated type ink jet recording head which minimizes stagnation of air bubbles in its ink flow paths. In view of the above problems associated with conventional ink jet recording heads and to solve this object, an improved ink jet recording head according to the independent claim 1 is provided. Further advantageous features, details and aspects of the invention are evident from the dependent claims, the description and the drawings. An ink jet recording head is formed by laminating a plurality of thin plate members having a plurality of ink flow paths partially formed therein. Each ink flow path extends continuously so as to reach a nozzle opening from an ink supply section via a pressure producing chamber. In such ink jet recording head, communicating holes formed in the respective thin plate members to enable the pressure producing chamber to communicate with the nozzle opening are linearly arranged. As a result of this construction, the ink from the pressure producing chamber can flow without stagnating in the communicating holes in the thin plate members, so that the air bubbles in the ink can be discharged from the nozzle openings effectively. An ink jet recording head which can be employed in a recording head having a plurality of nozzle opening arrays, preferably three or more, and which can minimize inter-line distance error to ensure high-quality printing, comprises a plurality of nozzle opening arrays, arranged in an auxiliary scanning direction, which is substantially perpendicular to the main scanning direction. The nozzle opening arrays are divided into groups, preferably three groups, and spaced at predetermined intervals in the main scanning direction. In such ink jet recording head, nozzle openings of the groups are arranged on both sides of a group arranged in the middle of the recording head supplement spaces between these nozzle openings of the middle array. Furthermore, a nozzle opening of the group arranged in the middle is positioned uppermost or lowermost on the face of the print head, so that lines printed by the nozzle openings of the groups arranged on both sides interpose the lines printed by the nozzle openings of the middle group. As a result, the maximum distance between nozzle openings printing adjacent lines in the main scanning direction can be equal or substantially equal to half the maximum distance between the nozzle opening arrive at both sides of the print head. Therefore, inter-line positional error is reduced. These and other objects and advantages of the invention will become more apparent and more readily appreciated from the following detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, of which: Fig. 1 illustrates an embodiment of the nozzle opening arrays of an ink jet recording head of the present invention; Fig. 2 is an exploded perspective view showing the detailed assembly of the ink jet recording head of Fig. 1; Fig. 3 is a sectional view showing the ink jet recording head of the invention with the shifted position of a nozzle opening; Figs. 4A to 4D respectively show embodiments of the present invention wherein the position of a nozzle opening with respect to the corresponding pressure producing chamber is shifted by adjusting both the position of the nozzle opening and the positions of introducing holes connecting the nozzle opening to the pressure producing chamber in the embodiment of the ink jet recording head shown in Fig. 1; Fig. 5A illustrates a pattern printed by a recording head having nozzle opening arrays according to the present invention; and Fig. 5B illustrates a pattern printed by a recording head having nozzle opening arrays according to a conventional arrangement. Fig. 1 shows an exemplary embodiment of a nozzle opening arrangement of an ink jet recording head of the present invention. Nozzle plate 130 includes six arrays of nozzle openings A, B, C, D, E, F. The nozzle openings 1, 7, 13, 19 and 25 of the first array A are positioned closest to the center line of the nozzle plate 130. Nozzle openings 2, 8, 14, 20 and 26 of the second array B are positioned close to one lateral end of the nozzle plate 130, for example, at the left end, and the nozzle openings 3, 9, 15, 21 and 27 of the third array C are positioned between the first array A and the second array B. Nozzle openings 4, 10, 16, 22 and 28 of the fourth array D are positioned on a side of the first nozzle opening array A opposite to the side at which the third array is positioned. The nozzle openings 5, 11, 17, 23 and 29 of the fifth array E are positioned closest to the lateral end opposite to the lateral end at which the second array B is positioned, for example, the right end. Finally, the nozzle openings 6, 12, 18, 24 and 30 of the sixth array E are positioned closest to the fifth nozzle opening array E. These nozzle opening arrays axe divided into three groups. The first nozzle opening array A and the fourth nozzle opening array D constitute a first group 201. The second and third nozzle opening arrays B and C constitute a second group 202. The fifth and sixth nozzle opening arrays E and F constitute a third group 203. The nozzle openings of the respective groups 201, 202 and 203 communicate with the ink jet recording head unit, as shown in Figs. 2, 3A and 3B, so that the nozzle openings are supplied with ink to be jetted. The nozzle openings 1, 4, 7, 10, 13, 16, 19, 22, 25 and 28 of the first group 201 are arranged at a pitch of three dots apart in an auxiliary scanning direction, that is, in the vertical direction as viewed in Fig. 1. The pairs of nozzle openings 2 and 3, 8 and 9, 14 and 15, 20 and 21, and 26 and 27 of the second group 202 are arranged at a pitch of one dot apart, and are positioned in the vertical direction between or substantially between nozzle openings 1 and 4, 7 and 10, 13 and 16, 19 and 22, and 25 and 28, respectively. This pitch is repeated, for example, at a cycle of five pairs of dots. The pairs of nozzle openings 5 and 6, 11 and 12, 11 and 18, 23 and 24, and 39 and 30 of the third group 203 are arranged it a pitch of one dot apart, and are positioned in the vertical direction between or substantially between nozzle openings 4 and 7, 10 and 13, 16 and 19, and 22 and 25, and in the vertical direction below or substantially below nozzle opening 28, respectively. This pitch is repeated, for example, at a cycle or five pairs of dots. Fig. 2 is an exploded perspective view showing the assembly of an embodiment of the ink jet recording head of the present invention, as shown in Fig. 1. Figs. 3A and 3B are sectional views, each showing a structure in the vicinity of a pressure producing chamber that is connected to a single common ink chamber. As showing in Fig. 2, the ink jet recording head comprises piezoelectric vibration element drive sections 100, which are formed by mounting piezoelectric vibration plates 104, made of PZT or the like, onto a surface of a vibration plate 102 made of a zirconia (ZrO 2 ) thin plate member or the like whose thickness is about 10 µm. The piezoelectric vibrations plates 104 are mounted so as to oppose pressure producing chambers 103, which will be described below. A spacer 105, which is made of a ceramic thin plate member, such as a 150 µm-thick zirconia thin plate member or the like, has through holes 106 therein. These through holes 106 constitute the pressure producing chambers 103, which are thus formed at a predetermined pitch. The shape of each through hole 106 coincides with that of the pressure producing chamber 103. A board 108 is disposed adjacent the spacer 105 to close the corresponding ends of the pressure producing chambers 103. Introducing holes 109 and 111 are formed in board 108. Introducing holes 109 have a larger diameter than that of nozzle openings 131, which are formed in nozzle plate 130, and enable the nozzle openings 131 to communicate with corresponding pressure producing chambers 103. Introducing holes 111, on the other hand, enable their corresponding pressure producing chambers 103 to communicate with common ink chamber 110. These three members 100, 105, 108 are integrated into a single structure, and are mounted on a unit fixing plate 112 by adhesive or the like. The unit fixing plate 112 also acts as a flow path regulating plate in this embodiment. The unit fixing plate 112 includes flow path regulating holes 113, which are positioned between the introducing boles 111 and the common ink chamber 110 when the unit fixing plate 112 is mounted between the board 108 and the thermal deposition film 115, described below, as shown in Fig. 3B. Also, the unit fixing plate 112 includes introducing holes 114 which are positioned to oppose the through holes 109 when the unit fixing plate 112 is mounted to the board 108. Each flow path regulating hole 113 has a flow resistance substantially equal to that of the nozzle opening 131, and each introducing hole 114 enables the nozzle opening 131 to communicate with the pressure producing chamber 103. The thermal deposition film 115 bonds a common ink chamber forming plate 118, described below, to the unit fixing plate 112. The thermal deposition film 115 includes windows 116 and introducing holes 117. Each window 116 coincides with the common ink chamber 110, and each introducing hole 117 enables the nozzle opening 131 to communicate with the pressure producing chamber 103. The common ink chamber forming plate 118 includes windows 120 and introducing holes 121. The ink chamber forming plate 118 is, for example, a 150 µm-thick stainless steel plate member or the like, which is corrosion resistant and whose thickness is adequate to form the common ink chambers 110. Each window 120 is substantially V-shaped and thus corresponds to the shape of the common ink chamber 110. Each introducing hole 121 has a diameter larger than that of the nozzle openings 131, and enables their corresponding pressure producing chambers 103 to communicate with the nozzle openings 131. As described above, the nozzle openings 131 are formed in the nozzle plate 130. The nozzle plate 130 is fixed to the common ink chamber forming plate 118 by a thermal deposition film 133 or the like, so that the nozzle openings 131 communicate with their respective pressure producing chambers 103 through introducing holes 109, 114, 117 and 121, and through hale 134 farmed in the thermal deposition film 133. The diameter of these introducing holes 109, 114 and 121 is determined so that the opening at least on the side of the nozzle opening 131 is small. The laminated structure allows the nozzle opening 131 to communicate with the pressure producing chamber 103. The nozzle opening 131 is shifted by a distance ΔL, as shown in Fig. 3, nevertheless the ink is not likely to stagnate. Accordingly, air bubbles contained in the ink can be discharged swiftly from the nozzle opening. That is, if the nozzle openings 131 are shifted in a direction toward one end of the pressure producing chamber 103 as shown in Fig. 4A, the nozzle opening 131 can be aligned near the end of the pressure producing chamber 103. If the respective introducing holes 109, 114, 121, for example, are sequentially shifted in any direction with respect to the pressure producing chamber 103, as shown in Figs. 4B, 4C, then the pitch between the adjacent nozzle openings 131 can be adjusted arbitrarily. Alternatively, as shown in Fig. 4D, the pressure producing chambers 103 may be arranged to communicate with nozzle openings 131 which are positioned asymmetrically on, the nozzle plate 130. In the embodiment of the recording head of the present invention, when a drive signal is applied to the piezoelectric vibration plates 103, the vibration plate 102 is flexed, thereby causing the pressure producing chambers 103 to contract. As a result, the ink within the pressure producing chambers 103 is jetted to the nozzle openings 131 via the introducing holes 109, 114, 117 and 121, and is jetted therefrom in the form of an ink droplet. When the drive signal is removed after the ink droplets have been jetted, the piezoelectric vibration plate 104 returns to its original position, thereby causing the pressure producing chamber 103 to expand to its original size. As a result, an amount of ink corresponding to the amount of ink jetted out of the nozzle openings 131 flows into the pressure producing chamber 103 from the common ink chamber 110 via the flow path regulating holes 113 and the introducing holes 111. This cycle is repeated until the amount of ink droplets necessary for printing have been jetted. Operation of this embodiment of the recording head having the nozzle opening arrangement of the embodiment shown in Fig. 1 will now be described with reference to Fig. 5A. Fig. 5A is an exemplary diagram illustrating the correspondence between the position of lines printed in a print line (e.g, a single character line) in the horizontal direction and the nozzle openings that print such lines of the print line. This figure also illustrates the position of some of the nozzle openings that print the uppermost lines in an adjacent print line. The number in each circle corresponds to the number assigned to a nozzle opening in Fig. 1. Lines in a print line are printed at an interval of three dots by the nozzle openings 1, 4, 7, 10, 13, 16, 19, 22, 25 and 28 of the nozzle opening arrays A and D of the first group 201. Two lines are printed by the nozzle openings 2, 3, 8, 9, 14, 15, 20, 21, 26 and 27 of the nozzle opening arrays B and C of the second group 202, so as to supplement lines between the odd-numbered nozzle openings and the even-numbered nozzle openings of the first group 201, i.e., between nozzle openings 1 and 4, 7 and 10, 13 and 16, 19 and 22, and 25 and 28. Two lines are similarly printed by the nozzle openings 5, 6, 11, 12, 17, 18, 23, 24, 29 and 30 of the nozzle opening arrays E and F of the third group 203, so as to supplement the lines between the even-numbered nozzle openings and the odd-numbered nozzle openings of the first group 201, which are not supplemented by the second group 202, i.e., between nozzle openings 4 and 7, 10 and 13, 16 and 19, 22 and 25, and vertically below 28. With the nozzle openings of the second and third groups 202 and 203, respectively, being arranged on both sides of the nozzle plate 130 to print lines which interpose the lines printed by the nozzle openings of the first group 201, arranged in the middle of the nozzle plate, the maximum distance in the main scanning direction between any two nozzle openings that print vertically adjacent lines is equal to half or substantially half the distance between groups 202 and 203 arranged on both sides of the nozzle plate 130. For this reason, an error that occurs when the vertical direction of the nozzle openings in the recording head is not parallel with the sheet forward direction, but is slightly at an angle with respect to the carriage, is substantially halved. That is, assuming that the distance in the main scanning direction between the nozzle opening arrays 202 and 203 is G, and that the angle of inclination of the head is , an error G x sin is substantially halved. In addition, since the nozzle openings are arranged so that the uppermost line in a print line is printed by a nozzle opening of the first group 201, that is, nozzle opening 1 in this embodiment, and the lowermost line in a print line is printed by a nozzle opening of either group 202 or 203 (i.e., nozzle opening 30 in this embodiment), the distance in the main scanning direction between the nozzle openings that prints the lowermost line of the print line (i.e., nozzle 30), and the upper most line of the next print line (i.e., nozzle 1), is also equal to half or substantially half the distance between groups 202 and 203. This, in turn, halves or substantially halves the error that may occur between the print lines that are printed before and after sheet forwarding, and thus prevents a white line or a black line from being produced, as often is the case in conventional printers. That is, in a conventional print head having a nozzle opening arrangement as shown in Fig. 5B, adjacent lines printed by the nozzle openings arranged on opposite sides of the print head (e.g., the nozzle openings 6 and 7 of the nozzle opening arrays A' and F') result in a large print error when the direction of the nozzle opening arrays A' through F' is not parallel to the sheet forwarding direction. This error occurs because the distance between these nozzle openings in the main scanning direction is equal to the distance between the nozzle opening arrays A' and F'. In addition, because this large distance in the main scanning direction exists between nozzle openings 1 and 30, when the direction of the nozzle opening arrays is not parallel to the sheet forwarding direction, a large error will occur between a print line and a subsequent print line printed after the sheet is forwarded.

Claims: An ink jet recording head comprising a plurality of thin plate members (108,112,118) each having a plurality of holes (109,114,121) therein, said thin plate members (108,112,118) being laminated together so that said holes (109,114,121) formed in adjacent said thin plate members (108,112,118) cooperate to form a plurality of ink flow paths each continuously extending from a respective nozzle opening (131) to a respective pressure producing chamber (103) which communicates with an ink supply section (110), characterized in that said holes (108, 112, 118) are shifted with respect to each other, and the areas of the holes (109,114,121) of the thin plate members (108,112,118) arranged in succession towards said nozzle openings (131) become smaller such that the areas of the holes (109,114,121) of the thin plate member (108,112,118) closest to the nozzle openings (131) are smallest and the areas of the holes (109,114,121) of the thin plate members (108,112,118) further away from the nozzle openings (131) are largest. An ink jet recording head as claimed in claim 1, characterized in that said holes (109,114,121) of said adjacent thin plate members (108,112,118) are sequentially shifted outward with respect to each other in a manner towards said nozzle openings (131) such that the holes (109,114,121) of said thin plate member (108,112,118) closest to the nozzle opening (131) is at a maximum shifted distance with respect to the holes (109,114,121) of the thin plate member (108,112,118) furthest from the nozzle opening (131). An ink jet recording head as claimed in one of the preceding claims, characterized in that said ink flow paths, nozzle openings (131) and pressure producing chambers (103) are grouped into ink flow path units, said ink flow path units being arranged so that the nozzle openings of one of said ink flow path units are positioned between the nozzle openings of another one said ink flow path units.

Inventors: ISHII TAKAYUKI, KITAHARA KOHEI, ISHII, TAKAYUKI, KITAHARA, KOHEI
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1994
Main classification: B41J2
IPC codes: B41J2